Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) No. H06-345417, i.e., JP 06-345417 A (“Patent Reference 1”) discloses a process in which a coating composition that consists of a hydrogen silsesquioxane diluted with a solvent and a filler (such as glass, alumina, silica, colloidal silica, or titanium dioxide) is applied onto an electronic substrate (e.g., onto a substrate of a silicon wafer or a CMOS device), and then a ceramic film is formed by heating the coating for 45 minutes to 2.5 hours in air at a temperature of 50° C. to 800° C. The present inventors herein have found that since the filler contained in the aforementioned coating composition begins to precipitate immediately after preparation of the composition, the coating composition must be used for coating immediately after preparation, and if the coating composition containing the aforementioned precipitate is used for coating, a formed ceramic film will have defects such as non-uniformity and unevenness.
Kokai No. H11-106658, i.e., JP 11-106658 A (Patent Reference No. 2) discloses a process in which a hydrogen silsesquioxane resin composition that contains from 1 to 100 parts by weight of a colloidal silica (with average size of particles not exceeding 100 nm) per 100 parts by weight of the hydrogen silsesquioxane is applied as a coating onto semiconductor devices, electric devices, optical elements, or the like, and then cured in order to form silicon oxide films, such as silica-type films, with excellent insulating properties and optical transmittance. The aforementioned hydrogen silsesquioxane composition is produced by dispersing colloidal silica in an organic solvent, dissolving the hydrogen silsesquioxane in a solvent in a separate process, and then mixing both liquids.
However, the present inventors herein have found that a mixture of an organic solvent dispersed with colloidal silica and a solution obtained by dissolving a hydrogen silsesquioxane resin in a solvent begins to form precipitates within a few minutes after mixing, and, therefore, the mixture should be immediately used for coating; otherwise, a formed silicon oxide film will have defects such as non-uniformity and unevenness.